Bilayer dielectric composites with positive-ε and negative-ε layers achieving high dielectric constant and low dielectric loss

•A novel design of bilayer composite is prepared with positive-ε and negative-ε layers.•The introduction of negative-ε layer realizing the permittivity boost.•The positive-ε layer provides low dielectric loss via adding BN sheets.•The design strategy has great importance in exploration of energy storage materials.